I had just done this to mine with great results. The bumpers were really light gray and faded so I took a heat gun to them and they come up like new seriously it's like witch craft or something haha. I know it's not a new idea and most of you probably already know about it but look it up on youtube if not

Ah cool, yeah I heard smooth peanut butter works really well too. The heat gun method is not going to win any shows but it definitely smarten it up. Time will tell if it goes all streaky after a while but it can be redone. Just make sure it's perfectly clean and free from oil streaks or anything before you start :-)